Are you using the default user interface? If not, be mindful that there was a patch a few days ago which modified some advloot windows. Be sure to update your custom UI.
This happened to me twice last night. After luckily getting in a third time I tried very hard not to reproduce the problem, but this is definitely what tripped it both times. I used advanced loot for about another six hours before logging, didn't get near that button, and had no more crashes. Stock UI here, nothing custom.
